import type {Type} from '../types';
import type {Expression} from '../expression';
import type {ParsingContext} from '../parsing_context';
import type {EvaluationContext} from '../evaluation_context';

export class Var implements Expression {
    type: Type;
    name: string;
    boundExpression: Expression;

    constructor(name: string, boundExpression: Expression) {
        this.type = boundExpression.type;
        this.name = name;
        this.boundExpression = boundExpression;
    }

    static parse(args: ReadonlyArray<unknown>, context: ParsingContext): Expression {
        if (args.length !== 2 || typeof args[1] !== 'string')
            return context.error(
                "'var' expression requires exactly one string literal argument."
            ) as null;

        const name = args[1];
        if (!context.scope.has(name)) {
            return context.error(
                `Unknown variable "${name}". Make sure "${name}" has been bound in an enclosing "let" expression before using it.`,
                1
            ) as null;
        }

        return new Var(name, context.scope.get(name));
    }

    evaluate(ctx: EvaluationContext) {
        return this.boundExpression.evaluate(ctx);
    }

    eachChild() {}

    outputDefined() {
        return false;
    }
}